Pediatric overweight is a serious public health problem that is increasing in prevalence, particularly among minority children from low-income families. Although there has been much attention directed toward overweight prevention programs administered through the schools, most programs have not been effective in halting the accumulation of body fat that occurs during adolescence. The objectives of this application are to develop and implement a multilevel small group and school-wide intervention to prevent overweight among adolescent females by increasing consumption of healthy foods (fruits and vegetables) and time spent in physical activity. This application extends a recently completed randomized trial of a home and community-based health promotion/overweight prevention program (the Challenge Program), conducted by assigning college mentors to low-income, urban African-American adolescents. Adolescents enrolled in the intervention were statistically less likely to become overweight than adolescents in the control group over the 18-month study period. In the proposed project, the Challenge Program, which is based on developmental-ecological and social cognitive theory, has been extended to a small group format and pilot tested in schools. The proposed program retains many of the elements of the original program, including the college mentors, family and community modules, and collaboration with two urban YMCAs. The primary aim of the proposed project is to use a factorial design to compare a multi-level (school and small group) intervention with school-only, small group-only, or no intervention on body composition, diet, and physical activity among 800 low-income, urban, minority 12- 13 year old girls from 10 middle schools. The second aim is to examine whether the impact of the intervention on body composition, diet, and physical activity varies by: 1) family and peer support for adopting a healthy diet and engaging in physical activity or 2) stage of change for diet and physical activity. The final aim is to examine whether the impact of the intervention on adolescents' body composition, diet, and physical activity is mediated by changes in self-efficacy. In addition to evaluating the intervention, findings from the proposed study will enhance our understanding of how family and peer support, stage of change, and adolescents' self-efficacy for diet and physical activity are related to changes in body composition. Public Health Relevance: The objective of this application is to evaluate whether small group and school-wide interventions among 12-13 year old females in urban middle schools are effective in increasing consumption of healthy foods (fruits and vegetables) and time spent in physical activity. The 12-session small group intervention will be implemented by college mentors in collaboration with the YMCA and the school-wide intervention is a partnership among school personnel, students, parents, community members, and university representatives. Positive findings would suggest that interventions to prevent overweight among middle- school females should include school-wide and small group components with family, school, and community involvement.